Supporting stockings used to overcome the described problems are known in a lot of variations, and are on the market in a lot of models and sizes. However, they are all passive, meaning that they are produced with a given elasticity that will decrease over time. Typically, support stockings can be used for about 6 months, whereafter they have lost the major part of their elasticity.
Support stockings that are inflatable are also known, and they are able to add a well-adjusted compressive force to a body extremity such as a leg. A pneumatic device inflates each compartment in the stocking to a given level of pressure, and this pressure is maintained for a given period. This type of stockings is, however, only useable in a controlled environment, like a hospital or in the home of a permanently sick person, and is only to be used during periods where the person is in a resting position.
All these kinds of stockings may be called passive, since they give a predetermined compressive force being constant, except for loosing elasticity due to wear. An advantage could be obtained if the compressive forces were controllable in some way. This is the case in U.S. Pat. No. 6,123,681, where the stocking contains polymer of the kind constricting if exposed to some stimulus, preferable electric. By splitting the polymer into a plurality of strips, each being controlled individually, compressive forces may be generated sequentially along the length of the stocking to stimulate fluid flow, such as blood. The power source making the stimulations is then possible programmed in some way, like to make the individual polymer strips constrict in a cyclic order.